With the development of technologies, 3G technologies have already been widely applied, such as WCDMA (Wideband Code Division Multiple Access), CDMA2000 (Code Division Multiple Access 2000) and TD-SCDMA (Time Division-Synchronous Code Division Multiple Access).
However, 2G networks have been constructed for a long time, so coverage of the 2G networks is better than coverage of 3G networks, and this phenomenon will not change in the short term. Therefore, most of current 3G terminals are 2G/3G dual-mode mobile phones supporting a 2G network and a 3G network simultaneously, such as a WCDMA/GSM (Global System of Mobile communication) dual-mode mobile phone, and a TD-SCDMA/GSM dual-mode mobile phone.
Generally, an existing 2G/3G dual-mode terminal preferably camps in a 3G network, and when a coverage problem occurs in the 3G network, the terminal reselects or is handed over to a 2G network, and when the 3G network is restored to normality, the terminal reselects or is handed back over to the 3G network. That is, the terminal performs a location update between the 2G network and the 3G network. However, a process in which the terminal frequently performs location updates will cause frequent access to a network element (such as a home subscriber server (HSS) or home location register (HLR)) of a core network, which results in overload of the network element of the core network.